1. Field of the Invention
The present invention relates to the field of well fluid removal. More particularly, it relates to the removal of well fluid using pressurized gas available in the well bore.
2. Description of Prior Art
The accumulation of liquids in oil and natural gas well casings restrict the flow of fluids from the producing formation to the bore hole by exerting pressure on the face of the producing formation. Several methods of removal have been devised for removal of liquids from a bore hole, each having their own particular advantages and disadvantages. One method is by dipping the liquid out of the casing with a long bucket or "swab" operated by a cable from a truck-mounted winch.
During the initial production of an oil well often the gas pressure in the reservoir is sufficient for the oil well to flow naturally. In the production life of a flowing oil well, a point will be reached wherein there is insufficient gas pressure to overcome the hydrostatic head created by fluid accumulation in the well bore principally because of the decrease in reservoir gas pressure. Another contributing factor to the well's ability to flow is the accumulation of formation water in the well bore which will produce a fluid hydrostatic head equal to the pressure of the gas which enters the reservoir. To maximize the returns from an oil/gas well, it is important to conserve the gas in the reservoir because the gas content is the primary motive source pushing the oil to the well bore. As a well becomes watered out or the formation gas is depleted to the extent that production is seriously reduced or terminated, it is necessary to periodically swab the well or install mechanical gear to pump liquid from the bore hole to reduce the hydrostatic head. Either operation decreases the economic efficiency of the oil or gas well, requires additional supervision and the utilization of expensive equipment.
Another gas lift system consists of placing a tubing down the center of the bore hole, then one can pump the well by intermittently injecting gas from an external source either into the bore hole or the well casing to propel the oil either up the well casing or the tubing.
Another method is to place small holes in the tubing at appropriate intervals and the oil will flow from the bore hole into the tubing. The gas delivered through the tubing will bubble the oil to the top and out of the bore hole. This method is not very efficient and it requires a large ratio of the gas volume used to the volume of liquid lifted.
A device patented by Hart discussed in U.S. Pat. No. 3,408,949 is a downhole float tube encircling the lower end of production tubing which moves vertically to intermittently produce fluid from the well. This device is designed to pump slugs of liquid at a time. While his device is to operate automatically downhole, it is obvious that sand and grit reduces the reliability of this device. Inertia of operation of the float tube will tend to waste gas with each cycle. Sand and the dirty well bore will obviously be very detrimental to the operation of this mechanical apparatus. Last but not least, a malfunction may require one to pull all of the tubing and the apparatus from the bore hole to correct the malfunction.
The autoswab invented by Gramling and discussed in U.S. Pat. No. 4,070,134 utilizes natural gas pressure to operate a free-floating pressure-sensitive swab to automatically remove fluids from well casings. The bore hole environment with sand and paraffin presents difficulties for these mechanical devices.
Jack pumps are the most used devices to lift oil and water from oil and gas wells. Unfortunately, this method is capital intensive and requires considerable maintenance. It also requires heavy equipment to pull and insert the tubing, rods and to move the jacks.